• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.302-311
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• 2022

Sound barrier walls are one of the most effective alternatives for reducing environmental noise on roads and railways in the city center. The insertion loss of the sound barrier against road traffic noise is the sum of the sound transmission loss, sound absorption loss, and sound energy reduction due to the diffraction attenuation of the sound barrier. The sound transmission loss of the sound barrier is one of the important factors that determine the insertion loss of the sound barrier and is a basic indicator that determines the performance of the sound barrier. Nevertheless, there is not a separate standard in Korea for measuring the acoustic transmission loss of sound barrier panels. There are only a few conditions in KS F 4770 series that stipulates on the general material of sound barrier panels. This thesis examines the necessity of the acoustic transmission loss measurement and evaluation standards of sound barrier walls, and seeks a measurement method in a free sound field (anechoic chamber) sound receiving room considering the characteristics of sound barrier walls installed in external spaces, unlike indoor building materials. In addition, a single number evaluation method using a reference spectrum was proposed so that the sound insulation effect according to various installation places such as roadside or railroad side can be easily displayed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.246-253
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• 2010

In this paper, a method of removing the space skew and cross-talk cancellation is proposed where the self-generated signals from the subject are used to obtain the subject's location. In the proposed method, the good spatial sound image is maintained even when the listener moves from the sweet spot. Two major parts of the proposed method are as follows: listener position tracking using the stimuli from the subject and removal of the space skew and cross-talk signals. Listener position tracking is achieved by estimation of the time difference of arrival (TDoA). The position of the listener is then computed using the Talyer-series estimation method. The head-related transfer functions (HRTF) are used to remove the space skew and cross-talk signals, where the direction of the HRTF is given by the one estimated from the listener position tracking. The performance evaluation is carried out on the signals from the 100 subjects that are composed of the 50 female and 50 male subjects. The positioning accuracy is achieved by 70%~90%, under the condition that the mean squared positioning error is less than $0.07m^2$. The subjective listening test is also conducted where the 27 out of the 30 subjects are participated. According to the results, 70% of the subjects indicates that the overall quality of the reproduced sound from the proposed method are improved, regardless of the subject's position.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.22-28
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• 2001

This paper describes the implementation of a robust speaker position location system using the voice signal received by microphone array. To be robust to the reverberation which is the major factor of the performance degradation, low-frequency phase restoration algorithm which eliminates the influence of reverberations using the low-frequency information of the CPSP function is proposed. The implemented real-time system consists of a general purpose DSP (TMS320C31 of Texas instruments), analog part which contains amplifiers and filters, and digital part which is composed of the external memory and 12-bit A/D converter. In the real conference room environment, the implemented system that was constructed by the proposed algorithms showed better performance than the conventional system. The error of the TDOA estimation reduced more than 15 samples.

• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.258-264
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• 2010

In this paper, we propose an objective quality feature which is based on the human auditory system to measure vacuum cleaner noise. It is observed that some frequency bands are more sensitive to the human auditory system. Therefore, we divided the audible frequency range of vacuum cleaner noise into a number of frequency bands and the average energy of these bands was calculated. Among a number of average energies, an average energy of a frequency band was selected as the proposed feature. In order to test the performance of the proposed feature, fourteen vacuum cleaners were chosen and the noise was recorded in an anechoic-chamber. Then we performed subjective tests to obtain subjective scores of the noise data using the PCM (paired comparison method) and ACR (absolute category rating) subjective methods. The proposed objective quality feature shows high correlation with the subjective scores.

• The Journal of the Acoustical Society of Korea
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• v.32 no.4
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• pp.335-345
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• 2013

The present study investigates the effect of the inter-aural level difference(ILD) on the syllable articulation test in classrooms which can be occurred by the absorption of interior surfaces. In order to do this, the sound absorbing materials were installed in the classroom and sound pressure level(SPL) at each ear was measured using binaural recording systems. Also, syllable articulation tests were carried out at a classroom with and without sound absorption materials by 20 students who have normal hearing condition, in order to investigates the effect of the ILD on the speech intelligibility. As a result, it was found that the larger inter-aural level differences was occurred at the nearer positions to lateral walls after sound absorptions were applied to lateral walls in the classroom. At some places, the measured ILD was lager than JND of sound level (3dB). Also, it was shown that the correlation coefficient of inter-aural level difference with the score of syllable test has the significant result(-0.441). Thus, It is concluded that ILD can affect the subjective speech intelligibility in classrooms.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.236-241
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• 2007

Recently, in accordance with the cultural progress and the improvement of citizen's consciousness level, it is the real situation that the construction of small-scaled Multi-Purpose Hall where various cultural events could be performed, is on increasing. However, because the most of Multi-Purpose Hall had been designed and built up without any consideration on Acoustic Factor, many problems are on occurring thereat. Because those small-scaled Multi-Purpose Hall have been mostly used with the finishing material which contains a high degree of Acoustic Absorption indiscreetly, both diffusion and reflection of sound are not establishing properly, and since the reverberation of sound is very low, in case of musical performance by musical instrument, its sound hears too arid and stiff, there occurs some acoustic defect such as it becomes difficult for music appreciation with sufficient timbre, so that the capability improvement on the matter is urgently requiring situation. On this viewpoint, this Research has caught the Authenticity of the forecasted value and actually measured value using Acoustic Simulation on the subject of the small-scaled Multi-Purpose Hall, and then intended to propose the optimum acoustic condition on the basis of the Authenticity. As the result, it could be designed a Multi-Purpose Hall equipped with the satisfactory acoustic performance compare with the time before improvement, so that it is considered that such research result could be practically used as the fundamental material when design for other similar small-scaled Multi-Purpose Hall in the future.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.369-377
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• 2018

This study investigated the effect of noise and reverberation on subjective measure of speech transmission performance for elderly person with hearing loss in residential space through listening test. Floor impact, road traffic, airborne, and drainage noise were employed as the residential noise, and several impulse responses were obtained through room acoustical computer simulation for an apartment building. Sound sources for the listening test consisted of residential noises and speech sounds for boh the young (the original sound) and the aged (the sound filtered out by filters with frequency responses of hearing loss of 65 years elderly person). In the listening test, subjects evaluated speech intelligibility and listening difficulty for the presented word ($L_{Aeq}$ 55 dB) at three noise levels ($L_{Aeq}$ 30, 40, 50 dB) and three reverberation times (0.5, 1.0, 1.5 s). Results showed that the residential space with noise level lower than equal to 50 dB ($L_{i,Fmax,AW}$) for jumping noise and 40 dB ($L_{Aeq}$) for road traffic, airborne, and drainage noise had speech intelligibility of 90 % and over and listening difficulty of 30 % and below. Speech intelligibility and listening difficulty for the aged sound source was shown to be 0 % ~ 5 % lower and 2 % ~ 20 % higher than those for the young sound source, respectively.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.292-299
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• 2018

The vehicle exterior design is the main parameter of aerodynamic wind noise, but the modification of it is nearly impossible at a proto-type stage. Therefore, it is very important to verify exterior design and estimate the correct wind noise level at the early vehicle design stages. The numerical simulations of aerodynamic wind noises around A-pillar and wiper were developed for specific vehicle exterior designs, but could not be directly used for the discussions with designers because these need complex modeling and simulation process. This study proposes new approach to A-pillar and wiper wind noise estimation at design stage using response surface methodology of modeFRONTIER, of which database is composed of PowerFLOW simulation, PowerCLAY modeling, SEA-Baced (Statistical Energy Analysis-Based) interior noise simulation, and turbulent acoustic power simulation. New design parameters are defined and their contributions are analyzed. A state-of-the-art, easy and reliable CAT (Computer Aided Test) tool for A-pillar and wiper wind noise are acquired from this study, which shows high usefulness in car development.

• The Journal of the Acoustical Society of Korea
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• v.32 no.1
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• pp.43-55
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• 2013

The window ventilation system based on the heat recovery device was developed which make air ventilation possible without opening the windows. However, mechanical and aerodynamic noises were come to pass which annoyed people in rooms. In the present study, noise of new window ventilation system was measured in both general room and anechoic chamber. Also, the noise path was detected to find cause of noise generation and vulnerable area of the device. Sound absorptive and insulation materials were applied to mitigate the noise. Finally, an alternative noise control method was suggested which can satisfy with the indoor noise standards. As a result, it was shown that the cause of noise was the low transmission loss in the ventilation system. As a result, it was shown that the main noise source of the ventilation system was the blower and the major cause of noise was the low transmission loss of the ventilation system. It is also concluded that the noise levels complies with the noise standards of 40 dBA when 2 mm rubber sheet is applied inside the ventilation system.

• Journal of the Korean Institute of Educational Facilities
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• v.28 no.3
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• pp.3-14
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• 2021

Speech information of teachers is transmitted to students in classrooms so that appropriate aural environment should be provided for academic purposes. Many researches have been undertaken for classroom acoustics, and acoustic standards of domestic classrooms were suggested based on the reverberation time and background noise level. However, these standards are suitable for middle and high schools and so not consider the auditory ability by ages. As a precedent research, the present study was begun to suggest an acoustic standard for lower grade elementary school classrooms with children under age 9 who have not normal auditory ability. In order to do this, acoustic performances of the lower grade classrooms were measured and compared with the general classrooms. Also, change of acoustic parameters depending on the desk layout was measured and analyzed. The measured acoustic parameters were background noise, signal to noise ratio, RT, STI, D₅₀, and IACC. As a result, it was found that background noise is exceed the standard of 35dB(A) at the schools along the road sides. Also, it was shown that most of acoustic parameters are higher in the classrooms built recently rather than the old classrooms. Generally, there are not much difference of acoustic parameters among the various desk layouts but, better acoustic performances are acquired at the center line and the seats near sound source. Also, Higher IACC was measured at the seats on the center line facing the source squarely.